Method of Laser Welding

ABSTRACT

A method of joining at least one first metal sheet and a second metal sheet by laser welding includes at least partially stacking the at least one first metal sheet and the second metal sheet on top of one another to form an overlap region and welding together the at least one first metal sheet and the second metal sheet in the overlap region along an oscillating line. Welding along an oscillating line creates a longer weld seam in comparison to welding along a straight line, thereby increasing the strength of the weld seam.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a National Stage of International ApplicationNo. PCT/EP2006/050129 filed on Jan. 10, 2006, which claims the benefitof German Patent Application No. 10 2005 001 606.5 filed on Jan. 12,2005. The entire disclosures of International Application No.PCT/EP2006/050129 and German Patent Application No. 10 2005 001 606.5are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a method for joining at least onefirst metal sheet and a second metal sheet by laser welding wherein thesheets are at least partially stacked on top of one another to form anoverlap region. The present disclosure also relates to a method forjoining at least three metal sheets by laser welding. The presentdisclosure further relates to the use of the methods and to a componentproduced by means of one of the methods.

The fuel consumption of motor vehicles increases with the weight to betransported. It is generally known in the vehicle industry, particularlyin the motor vehicle industry, that the increasing number of componentsused to provide the ever increasing comfort of a vehicle increases thecurb weight of a vehicle. Accordingly, in the vehicle industry, it isdesirable to optimize the weight of the components of the vehicle.

Furthermore, durability of the components in the vehicles under highloads (e.g., vibrations when driving a motor vehicle on uneven ground)and a high level of safety (e.g., in the event of an accident) isdemanded, and therefore, the components have to exhibit high rigidityand strength.

SUMMARY

One exemplary embodiment relates to a method of joining at least onefirst metal sheet and a second metal sheet by laser welding. The methodincludes at least partially stacking the at least one first metal sheetand the second metal sheet on top of one another to form an overlapregion and welding together the at least one first metal sheet and thesecond metal sheet in the overlap region along an oscillating line.

Another exemplary embodiment relates to a method of joining at leastthree sheets by laser welding. The method includes at least partiallystacking a first sheet, a second sheet and a third sheet on top of oneanother in such a way that they form an overlap region, providing alaser above the overlap region and welding together the first sheet, thesecond sheet and the third sheet in the overlap region along anoscillating line. The first sheet, the second sheet and the third sheetare stacked with decreasing thickness in the direction towards thelaser.

BRIEF DESCRIPTION OF THE DRAWINGS

It should be noted that the figures are merely exemplary and do notlimit the scope of the appended claims.

FIG. 1 a is a side view of a component produced by means of a laserwelding method according to an exemplary embodiment.

FIG. 1 b is a front view of the component of FIG. 1.

FIG. 2 shows a component produced by means of a laser welding methodaccording to another exemplary embodiment.

FIG. 3 shows the stacking and simultaneous welding of sheets withdecreasing sheet thickness in a direction towards a laser.

FIGS. 4 a and 4 b show the stacking and stepwise welding of sheets withdecreasing sheet thickness in a direction towards a laser.

FIG. 5 shows an embossing of a sheet and the arrangement of a weld seam.

FIG. 6 shows a first sheet with a flange on a second sheet.

FIG. 7 shows diagrammatically a comparison of the load-bearing strengthof several weld seams produced by means of the laser welding methodsdisclosed herein with a weld seam produced by means of a conventionalresistance spot welding method.

FIG. 8 shows a cross section of a component produced by means of a laserwelding method disclosed herein.

FIG. 9 shows a frame of a backrest for a motor vehicle seat produced bymeans of a laser welding method disclosed herein.

DETAILED DESCRIPTION

According to an exemplary embodiment, a method for joining at least onefirst metal sheet and a second metal sheet by means of laser welding isprovided. The sheets are at least partially stacked on top of oneanother to form an overlap region and are welded together in the overlapregion along an oscillating line after stacking.

For purposes of the present disclosure, use of the phrase “oscillatingline” is used broadly to refer to the line that a laser beam of a laserperforms on a sheet (e.g., metal sheet) facing towards the laser. Theperson skilled in the art understands that the contour of theoscillating line along which the sheets are welded together essentiallycorresponds to the contour of the weld seam created during welding.

As a result of welding along the oscillating line, the weld seam createdbecomes longer compared with welding along a straight line, whereby thestraight line corresponds to the projection of the oscillating line ontoan axis that intersects the oscillating line at least in two points.Since the weld seam created during welding of the sheets along theoscillating line is longer than the weld seam created during weldingalong a straight line, the strength of the weld seam is higher.

In view of the higher strength of its weld seams, a component producedby this method has a higher strength and rigidity, and is therefore bothmore durable and can withstand higher loads. On the other hand, thethickness of the sheets can thus be reduced, if necessary, so thatalthough the rigidity and strength of the produced component is nothigher or is not significantly higher, the weight of the component isreduced. The method of welding with an oscillating line thus permits anoptimization of the components with respect to their strength andrigidity on the one hand, and with respect to their weight on the otherhand.

According to an exemplary embodiment, the oscillating line has anessentially wave-shaped form. The person skilled in the art understandsthat other essentially random courses of the oscillating line are alsopossible (e.g., a curved, zigzag or round course of the oscillatingline). With a zigzag course of the oscillating line, however, stresspeaks may occur in the weld seam that may cause the weld seam to crack,while the stress curve with a wave-shaped or curved oscillating line ismore homogeneous. A round course, on the other hand, requires the laserand/or the sheets to be moved back. A zigzag or round course of theoscillating line may thus be less than optimal with respect to the speedduring the production of the weld seam and/or with respect to thetransport of the sheet(s). With a wave-shaped course, the laser and/orthe sheets can be moved uniformly so that the speed of assembly (e.g.,with respect to the welding times) is optimized.

According to an exemplary embodiment, the amplitude and/or wavelength ofa wave-shaped course of the oscillating line can be varied depending onthe space available for the component to be produced. The person skilledin the art understands that due to the contact-free method of laserwelding, this method can be employed in regions of components that areconsiderably more difficult to access than with other welding methodsthat require contact with the sheets to be welded (e.g., resistance spotwelding). In particular, as by contrast with resistance spot welding,laser welding requires access from only one side. The width of a regionof the component intended for welding (e.g., the width of a flange) cantherefore be chosen smaller than when welding by means of a weldingmethod requiring contact with the sheets to be welded. In particular,with a complex form of the sheets or of the component to be produced.The size of the sheet(s) required is thus smaller so that the weight ofthe component to be produced is reduced.

The strength of the weld seam and the rigidity of the componentincreases with an increase in the amplitude or a reduction in thewavelength of the wave-shaped oscillating seam due to the increase inthe length of the weld seam by comparison with a weld seam in a straightline. As such, the strength of the weld seam and the rigidity of thecomponent can be set by varying the amplitude and wavelength of theoscillating line.

According to an exemplary embodiment, the sheets have an overlap regionduring welding rather than being welded together by a butt weldingmethod in which they have to be placed very accurately against oneanother. Due to the welding along the oscillating line, which permits agreater tolerance for insertion of the sheets, no greater insertionaccuracy of the sheets is necessary than for the conventional resistancespot welding.

According to an exemplary embodiment, a laser is provided above theoverlap region of the sheets. According to another exemplary embodiment,the sheets are completely melted over their full thickness in the areaof the weld seam so that they form an essentially optimum joint onsolidification.

According to an exemplary embodiment, the oscillating line runs at anangle to the direction of the main load. For example, the oscillatingline may run essentially transversely to the direction of the main load.According to an exemplary embodiment, the oscillating line runs at anangle of approximately 45 degrees relative to the direction of the mainload. For purposes of the present disclosure, the phrase “direction ofthe main load” is used broadly to refer to the direction in which theweld seam is essentially loaded during use of the finished component.Providing the oscillating line at an angle to the direction of the mainload makes the strength of the resulting weld seam against forcesloading the component in or opposite the direction of the main loadhigher. The force that can be transmitted by means of the weld seam istherefore higher with a course of the oscillating line at an angle tothe direction of the main load, and may be particularly high with acourse at an angle of approximately 45 degrees.

According to an exemplary embodiment, the length of the oscillating lineis between 10 mm and 25 mm. For example, the length of the oscillatingline may be between 15 mm and 20 mm. The person skilled in the artunderstands that the length of the oscillating line is dependent on therequired strength of the weld seam and/or on the required strength andrigidity of the component and on the thickness of the sheets used.

According to an exemplary embodiment, the first sheet and the secondsheet have a different thickness and are stacked with decreasingthickness in the direction towards the laser. Depending on the clampingdevice employed, stacking of the sheets with decreasing thickness in thedirection towards the laser may also be advantageous since the thinnersheet has a lower rigidity than the thicker sheet, and hence thestacking of the thinner sheet on the thicker sheet and the subsequentclamping can be performed more easily and more quickly. The insertiontimes of the sheets during assembly are thus reduced.

According to another exemplary embodiment, at least three metal sheetsare at least partially stacked on top of one another in such a way thatthey form an overlap region and are joined together by means of laserwelding. According to an exemplary embodiment, all the sheets arestacked with decreasing thickness in the direction towards the laser andare then jointly welded together. According to another exemplaryembodiment, the at least two thickest sheets are stacked with decreasingthickness in the direction towards the laser and welded together, andthen the next thinner or the thinner sheets are stacked on the weldedthicker sheets with decreasing thickness in the direction towards thelaser and are welded to the latter. According to another exemplaryembodiment, the stacking of the thinner sheet(s) with decreasingthickness in the direction towards the laser on already welded thickersheets, and the subsequent welding of the stacked sheets in each case,is repeated several times until all the sheets are welded together.

The stepwise welding together of the sheets disclosed in theabove-mentioned second and third sub-point is advantageous with respectto the accessibility of the sheets during the assembly since laserwelding requires accessibility from only one side. In addition, thestepwise welding of the sheets allows a laser with a lower energy inputto be used than for the simultaneous welding together of all the sheets.The strength of the weld seam is maintained by using a laser with whichthe thickest sheets are essentially completely melted along theirthickness during welding. As the thicker sheets are already essentiallyoptimally welded to one another, it is only necessary to ensure duringwelding of thinner sheets that the weld seam of the thinner sheets to atleast the next thicker (adjacent) sheet is essentially optimal.

Simultaneous welding together of all the sheets, on the other hand,makes assembly faster.

When the at least three sheets are stacked with decreasing thickness inthe direction towards the laser, the use of laser welding ensures thatan optimal weld seam with respect to the strength is produced. Bycontrast with this method, provision of the most symmetrical structureof the sheets possible in the welding area is preferred when usingresistance spot welding so that when using three sheets of differentthickness, for example, the thinnest sheet is arranged in the middle sothat the distance between the contact surfaces of the sheets and the twoelectrodes is as equal as possible. Inert gas shielded arc weldingconventionally provides only for the welding of two stacked sheets.

According to an exemplary embodiment, an embossing is provided in atleast one sheet in the overlap region. The embossing equalizeswavinesses of the sheet(s) to be welded together and the sheets areessentially in contact with one another in the area of the embossing.The distance between the sheets is thus essentially minimal in the areaof the weld seam. According to an exemplary embodiment, the embossing isprovided in the thicker sheet as the thinner sheet can adapt more easilyto the contour of the thicker sheet.

According to an exemplary embodiment, the method of laser welding usingan oscillating line is used for the production of a component for avehicle (e.g., a motor vehicle). In particular, the method may be usedfor the production of a frame of a motor vehicle seat. Optimizedcomponents can be produced as a result of the method of welding alongthe oscillating line and the resulting high strength of the weld seamwith respect to its weight and its rigidity and strength. The methodthus requires no greater insertion precision of the sheets duringassembly than is necessary, for example, for conventional resistancespot welding. The strength of the weld seam is particularly high. Inparticular, the strength of the weld seam may be increased if thedirection of the main load is taken into consideration and theoscillating line is arranged at an angle to the direction of the mainload (e.g., an angle of approximately 45 degrees). The stacking of thesheets with decreasing thickness in the direction towards the laser maybe advantageous with respect to the accessibility of the sheets duringthe assembly. The simultaneous welding together of all the sheets isparticularly fast. This stacking may be simpler and faster with respectto the insertion and clamping of the sheets during assembly, and is thusinexpensive.

According to an exemplary embodiment, a component is produced by meansof the laser welding method using an oscillating line. According to anexemplary embodiment, the component is a frame of a motor vehicle seat.The person skilled in the art understands that the component can be arandom component in which the force to be transmitted by means of theweld seam is high and/or that is simple and quick to assemble.

According to an exemplary embodiment, the method can be used for bothmetallic sheets and for thermoplastic sheets.

Referring now to the FIGURES, and to FIGS. 1 a and 1 b in particular, acomponent produced by means of a laser welding method is shown accordingto an exemplary embodiment. FIG. 1 a shows a side view of the componentwhile FIG. 1 b shows a front view. The component is shown as including afirst sheet 1 and a second sheet 2. The sheets 1, 2 are at leastpartially stacked on top of one another so that they form an overlapregion 5. FIG. 1 a shows the arrangement of a laser 6 above the overlapregion 5 of the sheets 1, 2 and a laser beam 11 emanating from the laser6 during welding of the sheets 1, 2. Laser beam 11 is shown as strikingthe sheet 1 at a surface facing towards the laser 6. FIG. 1 b shows anoscillating line 4 along which the sheets 1, 2 are welded together. Thelength of the oscillating line 4, indicated diagrammatically by an arrow9, is longer than the length of a straight line indicated by an arrow 9′that corresponds to the projection of the oscillating line 4 onto anaxis passing through at least two points of the oscillating line 4. Anarrow 8 indicates the direction of a main load on a weld seam 4′ createdduring welding together of the sheets 1, 2 along the oscillating line 4(see FIG. 5). The direction of the main load 8 is arranged at an angle 7of approximately 90 degrees to the oscillating line 4.

Referring to FIG. 2, another component is shown according to anexemplary embodiment. Similar to the exemplary embodiment illustrated inFIGS. 1 a and 1 b, the exemplary embodiment illustrated in FIG. 2includes a first sheet 1 and a second sheet 2. However, in contrast tothe exemplary embodiment illustrated in FIGS. 1 a and 1 b, the exemplaryembodiment illustrated in FIG. 2 includes an oscillating line 4 arrangedat an angle 7 of approximately 45° degrees to the direction of the mainload 8. The arrow 8′ indicates the direction opposite the direction ofthe main load 8. FIG. 2 also shows diagrammatically the length of theoscillating line 9 and the length of the straight line 9′.

FIG. 3 shows the stacking and simultaneous welding of multiple sheets.According to the embodiment illustrated, three sheets, sheets 1, 2, 3with decreasing sheet thickness 10, 10′, 10″ in the direction towardsthe laser 6 (see FIG. 1), are welded together. The sheets 1, 2, 3 forman overlap region 5. Arranged above the overlap region 5 is the laser 6,indicated by the laser beam 11. According to an exemplary embodiment,the sheets 1, 2, 3 are welded together simultaneously.

FIGS. 4 a and 4 b show the stacking and stepwise welding of multiplesheets. According to the embodiment illustrated, three sheets, sheets 1,2, 3 with decreasing sheet thickness 10, 10′, 10″ in the directiontowards the laser 6, are welded together in a stepwise manner. Onceagain, laser 6 is indicated by means of a laser beam 11 and with respectto the sheet thickness 10, 10′, 10″ (see FIG. 3). FIG. 4 a shows thewelding of the two thicker sheets 1, 2 in their overlap region 5. FIG. 4b shows the subsequent welding of the thinnest sheet 3 to the twoalready welded thicker sheets 1, 2 in their overlap region 5′.

FIG. 5 shows an embossing 12 of a sheet 1 and the arrangement of a weldseam 4′ between the sheet 1 and a second sheet 2 essentially in contactwith the embossing 12. In the area outside the embossing 12, a distance13 between the first and the second sheet is essentially determined bythe depth of the embossing 12. According to an exemplary embodiment,distance 13 is between approximately 1/10 mm and approximately 8/10 mm.For example, the distance 13 may be approximately 5/10 mm. According toan exemplary embodiment, weld seam 4′ is provided inside the embossing12.

FIG. 6 shows a first sheet 1 with a flange 14 on a second sheet 2. Anarrow indicates a width 15 of the flange 14 required for welding of thesheets 1, 2 by means of a laser welding process using an oscillatingline. According to an exemplary embodiment, the width 15 is between 6 mmand 10 mm. For example, the width 15 may be approximately 8 mm.According to an exemplary embodiment, an embossing 12 (see FIG. 5) ismade in the area of the width 15 of the flange 14 indicated by the arrowon one of the two sheets 1, 2.

FIG. 7 is a graphic illustration showing a comparison of theload-bearing strength of several weld seams 4′ produced by means of thelaser welding method using an oscillating line (see FIG. 5), with a weldseam produced by means of a conventional resistance spot welding method.Illustration (a) shows the force that can be transmitted by the weldseam when the weld seam is produced by means of the resistance spotwelding method. The transmittable force is shown diagrammatically invertical direction on the scale and indicated by an arrow 16.Illustration (b) shows the force that can be transmitted by the weldseam when the weld seam is produced by means of a laser welding methodusing an oscillating line. The oscillating line 4 in illustration (b)has a length 9 of approximately 10 mm and an angle 7 of approximately 90degrees to the direction of the main load 8 of the weld seam 4′ (seeFIGS. 1 b and 2). As shown, the transmittable force of a weld seam 4′produced by means of the laser welding method using an oscillating lineis comparable with the transmittable force of a weld seam produced bymeans of the resistance spot welding method. Illustration (c) shows theforce that can be transmitted by the weld seam when the weld seam isproduced by means of a laser welding method using an oscillating lineand the oscillating line has a length 9 of approximately 20 mm. Asshown, the force that can be transmitted by means of the weld seam 4′ inillustration (c) is significantly higher than the force that can betransmitted by illustrations (a) and (b). The transmittable force can besignificantly increased once again if the oscillating line 4 is arrangedat an angle 7 of approximately 45 degrees to the direction of the mainload 8, as shown in illustration (d), and not at an angle 7 ofapproximately 90 degrees.

FIG. 8 shows a cross section of a component produced by means of a laserwelding method using an oscillating line. The component is made from aplurality of sheets 1, 2, 3 of different thickness. In order to ensureaccessibility to the necessary welding points, the first sheet 1 and thesecond sheet 2 are first welded together at a first welding point 41,whereby the sheets 1, 2 are arranged with decreasing thickness in thedirection towards the laser 6 (the laser 6 being indicated here by thelaser beam 11). The arrangement and/or clamping of the sheets 1, 2 isindicated by means of a tool mounting 16. In the second step, the thirdsheet 3 is welded to the first sheet 1 and the second sheet 2 at asecond welding point 42, whereby the third sheet 3 is thinner than thefirst and the second sheet 1, 2.

FIG. 9 shows a frame of a backrest of a motor vehicle seat produced bymeans of a laser welding method using an oscillating line. First pivotbrackets 17 of the seat made from the thickest sheet are arranged on aturntable (not visible here). A reinforcement frame 19 is then arrangedon the pivot brackets 17. The parts (i.e., first pivot brackets 17 andreinforcement frame 19) are clamped together and finally welded togetherby means of a laser welding method using an oscillating line. This isfollowed by positioning and clamping of a back panel 18 on the same oranother turntable (also not visible here) and welding to the alreadywelded reinforcement frame 19 and pivot brackets 17. The weld seam areashave an embossing 12 that is not visible here so that the distancebetween the sheets 17, 18, 19 is as small as possible in the area of theweld seam. According to an exemplary embodiment, the embossing 12 ismade in the thicker sheets in each case, in other words here in thepivot brackets 17 when welding the pivot brackets 17 to thereinforcement frame 19, and in the reinforcement frame 19 when weldingthe back panel 18 to the reinforcement frame 19. According to anexemplary embodiment, the back panel 18 can adapt very well to thecontour of the reinforcement frame 19 as it is very thin.

1. A method for joining at least one first metal sheet and a secondmetal sheet by laser welding, the method comprising: at least partiallystacking the at least one first metal sheet and the second metal sheeton top of one another to form an overlap region; and welding togetherthe at least one first metal sheet and the second metal sheet in theoverlap region along an oscillating line to form a weld seam.
 2. Themethod of claim 1 wherein the oscillating line has an essentiallywave-shaped form.
 3. The method of claim 1 further comprising providinga laser above the overlap region of the at least one first metal sheetand the second metal sheet.
 4. The method of claim 1 wherein theoscillating line runs at an angle to the direction of a main load,applied to the weld seam.
 5. The method of claim 1 wherein the length ofthe oscillating line is between approximately 10 mm and approximately 25mm.
 6. The method of claim 3 wherein the at least one first sheet andthe second sheet have a different thickness and are stacked withdecreasing thickness in the direction towards the laser.
 7. A method forjoining at least three sheets by laser welding, the method comprising:at least partially stacking a first sheet, a second sheet and a thirdsheet on top of one another in such a way that they form an overlapregion; providing a laser above the overlap region; and welding togetherthe first sheet, the second sheet and the third sheet in the overlapregion along an oscillating line, wherein the first sheet, the secondsheet and the third sheet are stacked with decreasing thickness in thedirection towards the laser.
 8. The method of claim 7 further comprisingproviding an embossing in at least one of the first sheet, the secondsheet and the third sheet in the overlap region.
 9. The method of claim7 wherein the method is used for production of a component for avehicle.
 10. (canceled)
 11. The method of claim 9 wherein the componentis a frame of a motor vehicle seat.
 12. The method of claim 4 whereinthe oscillating line runs substantially transverse to the direction ofthe main load.
 13. The method of claim 12 wherein the angle isapproximately 45 degrees.
 14. The method of claim 5 wherein the lengthof the oscillating line is between approximately 15 mm and approximately20 mm.
 15. The method of claim 7 wherein welding together the firstsheet, the second sheet and the third sheet comprises welding the firstsheet, the second sheet and the third sheet together after all of thesheets are stacked with decreasing thickness in the direction towardsthe laser.
 16. The method of claim 7 wherein stacking the first sheet,the second sheet and the third sheet and welding together the firstsheet, the second sheet and the third sheet comprises: stacking the twothickest sheets of the first sheet, the second sheet and the third sheetwith decreasing thickness in the direction towards the laser; weldingtogether the two thickest sheets; stacking the remaining sheet on thewelded thicker sheets with decreasing thickness in the direction towardsthe laser; and welding the remaining sheet to the welded thicker sheets.17. The method of claim 7 wherein stacking the first sheet, the secondsheet and the third sheet and welding together the first sheet, thesecond sheet and the third sheet comprises: selecting two sheets of thefirst sheet, the second sheet and the third sheet; stacking the selectedsheets with decreasing thickness in the direction towards the laser;welding together the selected sheets; stacking the remaining sheet onthe welded selected sheets with decreasing thickness in the directiontowards the laser; and welding the remaining sheet to the weldedselected sheets.
 18. A vehicle component comprising: a first sheet; asecond sheet at least partially stacked on top of the first sheet toform an overlap region; and a weld seam provided in the overlap regionfor securing the first sheet to the second sheet, the weld seam beingformed along an oscillating line.
 19. The vehicle component of claim 18further comprising a third sheet at least partially stacked on top ofthe second sheet, the third sheet having a thickness that is thinnerthan a thickness of the second sheet, which is in turn thinner than athickness of the first sheet.
 20. The vehicle component of claim 18further comprising an embossing in at least one of the first sheet andthe second sheet in the overlap region.
 21. The vehicle component ofclaim 18 wherein the weld seam is provided at an angle of approximately45 degrees relative to a main load applied to the weld seam.